The reason that I am not interested in establishing audibility limits is that my research concerns other areas. It is strictly directed at practical applications and at preferences of experienced (and modestly well off) listeners, however, i would like solid evidence that the extra cost is justified.

My ideal outcome would in each and every case be that no differences exists and I can use the cheapest and simplest solution and increase the profit.Ciao T

Hah! You wish!

And to make it just that wee bit more complicated, long gone is the rule of thumb that if you pay more, you get more. These days, the only rule is that there is no rule, you have to test just about everything yourself, and not once, but every time you get a new batch.

I've seen some serious variances in batches from some supposedly big names. I've seen warranty periods of some big and expensive names go down from 2 years to 6 months. And I'm supposed to give my customer a 5 year warranty?

There would be room to quibble. In some areas -110dB may be insufficient

This is where I can only but defer to the Golden Ears. If I put my ear right next to my speakers I can just about hear a hiss from the amplifier. It's certainly not audible to me more than a couple of inches away, even when not playing any audio - I imagine even Brownian motion of the air molecules probably swamps it after that. The idea that when playing music at any SPL, that level of underlying noise or distortion, even if completely non-harmonic, would be perceivable is, to me, incredible. And -110dB is much quieter than that!

The idea that when playing music at any SPL, that level of underlying noise or distortion, even if completely non-harmonic, would be perceivable is, to me, incredible. And -110dB is much quieter than that!

Bill Waslo's brilliant Sousa band demo is very enlightening in this regard.

Anyone remember the movie "The Ghostbusters"? The scene in which Harold Ramis and Dan Aykroyd are sitting on the steps of the university they have just been fired from and are discussiong their options, when Harold says something like:

When the first atronauts went to space, it was discovered that ball point pens will not operate at zero gravity. NASA immediately summoned all its staff on leave, cancelled some of its current projects and reallocated the resources, the current administration immediately passed a bill through congress and senate funding the project with $4 billion. 4 years later, they came out with a novel pen, costing $1,000 per unit, which works.

The Russians used a pencil.

One more similar story: during some international scientific conference they needed to calculate overnight percentage of land and ocean water on the Earth surface. Russian programmer printed globe strips on paper, took scissors, cut prints carefully, and weighted them. Soviet economy was very inertial: they could not give financing before planning. Plans were calculated for each 5 years, for the whole huge country, incuding education, resources, manufacturing, medicine, everything...
But they could give orders to do something "here and now", so engineers and scientists had to be creative in making results without resources.